BILBAO, Spain (Reuters) - BBVA's inquiry into allegations of spying involving Spain's second biggest bank could take several months to conclude, its executive chairman said on Friday as he sought to soothe concerns among retail investors.

Carlos Torres told shareholders in Bilbao that BBVA will cooperate with judicial authorities on the case and thanked his predecessor Francisco Gonzalez for stepping down as honorary chairman while awaiting the results of an internal investigation being carried out by auditors PwC.

The inquiry relates to jailed ex-police chief Jose Manuel Villarejo who media reports say was hired by BBVA to spy on top executives of a potential bidder for the bank, construction company Sacyr, and government officials in 2004 when Gonzalez was BBVA's executive chairman.

"It is in our interest to move forward as quickly as possible, but given the scope, PwC has told us that several months of work will be required before we see the first results," Torres, who replaced Gonzalez as executive chairman in January, told BBVA's annual shareholders meeting.

Sacyr's former chairman, Luis del Rivero, who was present at the annual general meeting, urged BBVA to set up a committee of banking sector experts to help win back its reputation.

"If the bank follows this recommendation it will save its reputation in a clean way," Del Rivero said.

Torres said the bank had so far not seen any significant impact on its banking business from the case, adding that BBVA will not reveal any details of its own inquiry while the case is being investigated by the Spanish authorities.

BBVA has acknowledged that it hired Grupo Cenyt, a security firm owned by Villarejo and that Cenyt provided various services to BBVA, but that the bank had found no evidence of spying.

The case was first reported in mid-2018 and was recognised by the bank in January when Torres sent a letter to staff addressing the allegations.

Villarejo was arrested in 2017 on money-laundering and other charges as part of a separate investigation.

Though the case was not officially on the agenda of the shareholders meeting in Bilbao, some retail investors expressed their discontent.

"We are facing a clear example of political power interference in the rules of market operations and corporate governance," said Jean Pierre Paellink, president of the World Federation of Investors, an association of small investors.

BBVA shares were up 1 percent at 1556 GMT, bringing their gains so far this year to 15 percent and outperforming other Spanish and European banks.